An apparatus for contracting a continuously corrugated material in the direction in which its ridges are juxtaposed to one another has been known. This kind of apparatus is, for example, used for reducing the pitch or distance between the riges defining the fins on a heat exchanger. The conventional apparatus includes a guide plate on which the lower side of a continuously corrugated material which is fed by toothed forming or feeding rollers is supported, and a braking plate pressing against the upper side of the corrugated material to create a frictional braking force to reduce the pitch between adjacent ridges.
The conventional apparatus has, however, the disadvantage that the contracted material cannot be controlled by its pitch between adjacent ridges. As the braking plate is pressed against the ridges of a corrugated material to contract it, the braking or contracting force caused by the braking plate should be varied with the height of the ridges and the variation of the contracting force makes the pitch between the ridges on the contracted material irregular. The conventional apparatus is, therefore, unusable for contracting a corrugated material having a varying ridge height.
Though a filter having a plurality of wavy portions which are provided in such a manner that a plurality of wavy portions forms a circle has already been invented, an apparatus for rounding a continuously corrugated strip of material for a filter element in order to make such filter has not been invented. Therefore, such an apparatus for rounding the continuously corrugated strip is eagerly required.
Though the filter having a continuously corrugated wavy portion arranged in such a manner that a plurality of wavy portions form a circle has been invented, the apparatus for shaping such filter automatically and quickly has not been provided. Therefore, such an apparatus for shaping the filter is eagerly required.